Microtome knife mount

ABSTRACT

A knife mount is proposed for a microtome to be used for cutting ultra-thin sections. The proposed mount is formed with a trough for coolant, such as liquid nitrogen, and provided with a heater, the mount, including trough and heater, being symmetrical about a plane therethrough and adapted to support a knife by way of a connection disposed in the plane of symmetry. This knife mounting arrangement reduces the effects of differential expansion and contraction on the knife cutting edge disposition. In a preferred arrangement the knife cutting edge is parallel to the plane of symmetry, and the mount co-operates with a specimen holder to provide relative feeding movement perpendicular to said plane, and relative cutting movement perpendicular to the cutting edge and parallel to said plane.

United States Patent 91 Hodson et ai.

[ 51 May 15,1973

[54] MICROTOME KNIFE MOUNT [73] Assignee: National Research Development Corporation, London, England [22] Filed: Apr. 6, 1971 [21] Appl. No.: 131,697

[30] Foreign Application Priority Data Apr. 7, 1970 Great Britain ..16,410/70 [52] US. Cl. ..83/l7l, 83/9155 [51] Int. Cl. ..G0ln 1/06 [58] Field of Search ..83/l71,9l5.5

[56] References Cited UNITED STATES PATENTS 3,191,476 6/1965 McCormick ..83/9l5.5 X

3,220,290 ll/l965 Shandon ..83/l 7l Primary Examiner-Frank T. Yost A tmrney-Cushman, Darby & Cushman [57] ABSTRACT A knife mount is proposed for a microtome to be used for cutting ultra-thin sections. The proposed mount is formed with a trough for coolant, such as liquid nitrogen, and provided with a heater, the mount, including trough and heater, being symmetrical about a plane therethrough and adapted to support a knife by way of a connection disposed in the plane of symmetry. This knife mounting arrangement reduces the effects of differential expansion and contraction on the knife cutting edge disposition. In a preferred arrangement the knife cutting edge is parallel to the plane of symmetry, and the mount co-operates with a specimen holder to provide relative feeding movement perpendicular to said plane, and relative cutting movement perpendicular to the cutting edge and parallel to said plane.

16 Claims, 1 Drawing Figure MICROTOME KNIFE MOUNT This invention relates to microtomes and more particularly to microtomes for providing sections from frozen specimens.

A microtome for this purpose, in which the microtome cutting assembly has a box-like freezer structure secured therearound, is referred to in a paper entitled Ultramicrotomy: a technique for cutting ultra-thin sections of unfixed frozen specimens for electron microscopy" by Dr. S.A. Hodson and Dr. J. Marshall and published in the Journal of Microtomy, 91, pages 105-117, 1970. This microtome is the subject of U.K. Pat. application No. 49021/68, and in a preferred form of the microtome, the knife holder comprises a trough for coolant, such as liquid nitrogen, for cooling the holder to a first temperature below that desired for op eration, and also an electrical heater for heating the holder to a second temperature higher than the first temperature, the supply of coolant and operation of the heater being controllable in response to an appropriately located transducer to substantially stabilize the knife temperature. In practice there will be a slight fluctuation of temperature about the equilibrium level determined by the transducer, but this can be held to an acceptable level. However, this temperature fluctuation will also be associated with alternate expansion and contraction of knife holder with resultant variation in the knife position. While this variation may be small, it can be significant when very thin sections, of the order of l,OOOA, and less, are to be cut.

An objection of the present invention is to reduce this difficulty and, to this end, there is provided a microtome knife mount formed with a trough for coolant and provided with a heater, the mount, including trough and heater, being symmetrical about a plane therethrough and adapted to support a knife by way of a connection disposed in said plane.

It will be appreciated that the plane of symmetry is substantially stationary, relative to the alternating expansion and contraction which arises from the temperature fluctuations at equilibrium with temperature control as discussed above, since the alternating dimensional changes occur symmetrically relative to the plane. Accordingly, the position of the knife is substantially unaffected by dimensional variations in" the mount about said plane.

The knife position can be affected by dimensional changes in the plane of symmetry itself within the mount, but the effect that this may otherwise have on the thickness of a section cut from a specimen can be substantially obviated by use of the mount in connection with a' knife and a specimen holder arranged to produce relative movement therebetween for feeding the specimen towards the knife edge in a direction perpendicular to the plane of symmetry. The directions of the knife edge and that of the relative movement between knife edge and specimen holder are. normally perpendicular to the specimen feeding direction, and so the former directions are conveniently parallel to the plane of symmetry of the knife mount in the present instance.

While it will be possible usually to employ this fuller geometry of mount, knife edge, and specimen feeding direction to obtain maximum reduction of the effects of dimensional variations due to temperature fluctuations, this is not essential. Basically, the present invention provides a knife mount in which the dimensional variations are substantially constrained to occur within a single plane, and the effects of such variations on knife edge position, and therefore section thickness, can be reduced by use of a mount which is relatively thin in the plane of symmetry, or by connecting the knife thereto at a location close to the datum or support position about which the relevant planar dimensional changes occur.

In practice the knife will be supported in a knife holder adapted for connection to the mount through the plane of symmetry of the latter while affording adequate thermal contact between the mount and holder on the one hand, and the holder and knife on the other hand, to permit stabilization of the knife temperature at the desired value. At this time, the thermal contact between the mount and the knife holder should not be so large relative to the thermal masses involved that the temperature fluctuations in the mount at equilibrium are substantially transmitted to the holder.

In order to further clarify the invention, an embodiment of the same together with associated knife holder, knife and specimen holder, is diagrammatically illustrated by way of example in the accompanying drawmg.

The illustrated mount 1 has a generally rectangular slabform base 2 with two upstanding generally triangular parts 3 and 4 extending transversely thereacross, one at one end of the base and the other at an intermediate position along the base. The base 1 is formed with a cavity therein at its other end to serve as a trough 5 for liquid coolant. The first-mentioned end of the mount is drilled to receive an electrical'heater 6, and the base portion between the parts 3 and 4 is drilled to receive a thermoelectric transducer 7.

The mount is integrally formed with its trough from lnvar, Cervit, or other suitable material having a coefficient of thermal expansion not more than per C.

' and the transducer 7 aresymmetricalabout the longitudinal medial plane of the former, this plane being denoted by chain line at 8.

The base portion housing the transducer forms, together with the'upstanding parts 3 and 4, a cradleto receive the knife holder.

A suitable form of knife holder is indicated as a metal block 9 recessed at 10 in itsupp'er face to receive a triangular section glass knife 11. The knife is seated on the floor of the recess 10 and held against one side wall of the recess by a'bolt 12 passing in threaded engagement through the opposite side wall. in this particular instance, the recess 10 is initially formed to be open at one end of the block 9, for convenience of machining, the open end then being closed adjacent the recess floor by a face plate 13 bolted across the relevant end of the block. This plate serves as a stop against which the knife is held by a further bolt 14 passing in threaded engagement through the closed end of the knife holder block. However, while this serves to give a predetermined positioning of the knife in its holder, the end-toend securement is in fact not essential in practice.

Securement of the knife holder in its mount is by seating the holder in the above mentioned cradle, with the knife cutting edge parallel to the plane 8, and by a bolt passing in threaded engagement through the part 4 of the mount to hold the knife holder against the part 3. The bolt 15 and its threaded bore are symmetrical about the plane 8, and the bolt 15 conveniently engages the head of bolt 12 securing the knife in its holder, the latter bolt being suitably recessed in the holder.

The base surface of the block 9 is angled slightly relaouter end to receive a specimen which is held in the chuck by a bolt 19. The chuck is therefore separable from the specimen holder body for freezing of the chuck with a specimen secured therein as described in application No. 49021/68. The body 16 is partly hollowed, with the hollow being continued upwardly by an extension 20 to define a trough 21 for liquid coolant. The rear of this extension serves to house a thermoelectric transducer 22 acting to control the supply of coolant to the trough 21, and thereby the temperature of the specimen holder, chuck and specimen, in predetermined manner. In this connection, it is to be noted that the chuck preferably acts as plug at the lower end of the trough 21 whereby the specimen is in close proximity to coolant in the trough.

As illustrated, the specimen holder is positioned for operation, with conventional or other suitable mechanisms, to effect a feeding movement of specimen towards knife, and a cutting movement for specimen relative to knife, in mutually perpendicular directions re,- spectively denoted by arrows 23 and 24 which are both perpendicular to the knife edge, and with the former also perpendicular to the plane of symmetry of the knife mount, but the-latter parallel to such plane.

Regarding materials of the additional components, the specimen holder is preferably made of the same material as the knife mount, and so also may the knife holder.

Features of the other parts of the microtome for use in association with the invention andnot discussed above can be as described in said application No. 4902 1/68. i I i In practice, temperature control preferably makes use of liquid nitrogen as coolant, this being stored in a suitable vessel fromwhich it is boiled off at a controlled rate by an immersion heater connected to a variable transformer. The heater boils offa head of nitrogen gas which escapes through a safety valve outlet from the storage vessel releasing gas at a controlled pressure of about 5 p.s.i. Since the specimen and knife are subject to individual temperature controls, there are two exit passages following the safety valve, each governed by a respective solenoid valve which opens and closes under the control of the respective thermoelectric transducer in the knife mount or specimen holder .as the case may be.

The specimen is cooled by dropping liquid nitrogen into the trough 21 under the control of transducer 22, suitable a platinum resistance thermometer with the resistor connected through a bridge circuit to a relay which opens and shuts the associated solenoid valve.

This system is set to maintain the nitrogen level above the axis of the specimen holder and so the operational temperature of the specimen approximates to that of the coolant. Specimen temperature can be controlled only relatively coarsely by varying the bridge resistance balanced against that of the transducer.

The knife temperature is controlled by a similar system, but differing by the addition of the heater 6 which is operated in alternating sequence with the relevant nitrogen supply solenoid valve by appropriate relay contacts. This leads to a finer control and the knife temperature is normally maintained at about l00C. compared to the order of l80C. for the specimen.

With operation such as described above, drift of the knife position due to fluctuations at equilibrium have been reduced to a maximum of about 10A per second, compared to the order of hundreds of Angstrom Units per second without use of the present invention.

We claim:

1. A microtome knife mount formed with a trough for coolant and provided with a heater, the mount, including trough and heater, being symmetrical about a plane therethrough and adapted to support a knife by way of a connection disposed between said trough and heater and in said plane.

2. A mount according to claim 1 comprising a base, two mutually spaced upstanding parts extending from one portion of said base to define a cradle with said base portion therebetween as the cradle floor and said upstanding parts as the cradle sides, a cavity formed in the remaining portion of said base to define a trough for liquid coolant, clamp means coupled with one of said upstanding parts to secure a knife in said cradle against the other of said upstanding parts, said base, upstanding parts, trough and clamp means being symmetrical about a common medial plane therethrough.

3. A mount according to claim 2 wherein said base is of generally slab form having said one upstanding part extending from one end of one major face thereof, said other upstanding part in the form of a wall extending from and across the intermediate region of said one major face, and said cavity formed in; the other end of said one major face.

4. A mount according to claim 2 comprising a thermoelectric transducer housed in said mount, said transducer being symmetrically disposed relative to saidplane.

'5. A mount according to claim 2 in combination with a knife holder in the form of a block recessed in its upper face toreceive a triangular section knife seated therein with its cutting edge portion extending above said block, said block being provided with second clamp means coupled with one side wall of said block and passing therethrough to said recess to secure said knife against the opposed side wall of said block.

6. A mount according to-claim 5 wherein the first mentioned and second clamp means comprise respective bolts, and said knife holder is dimensioned for disposition and securement in said cradlewith said bolts substantially axially aligned in said plane.

. 7. A mount according to claim 1 of integral construction.

8. A mount according to claim 1 made of material having a coefficient of thermal expansion not greater than 10* per C. at l00C.

9. A microtome knife assembly comprising: a cutting member,

a support member for said cutting member, which support member is formed with a trough for liquid coolant,

a heater connected with said support member in spaced disposition from said trough, and

connector means securing said cutting member to said support member at a position between said trough and said heater,

said support member, trough, heater and connector means being symmetrical about a common plane therethrough.

10. A microtome knife mount comprising:

a base,

two mutually spaced upstanding parts extending from one portion of said base to define a cradle with said base portion therebetween as the cradle floor and said upstanding parts as the cradle sides,

a cavity formed in the remaining portion of said base to define a trough for liquid coolant,

clamp means coupled with one of said upstanding parts to secure a knife in said cradle against the other of said upstanding parts, 1

said base, upstanding parts, trough and clamp means being symmetrical about a common medial plane therethrough.

l l. A mount according to claim wherein said base is of generally slab form having said one upstanding part extending from one end of one major face thereof,

said other upstanding part in the form ofa wall extending from and across the intermediate region of said one major face, and said cavity formed in the other end 0, said one major face.

12. A mount according to claim 10 comprising a thermoelectric transducer housed in said mount, said transducer being symmetrically disposed relative to said plane.

13. A mount according to claim 10 wherein said base and upstanding parts are of integral construction.

14. A mount according to claim 13 wherein said base and upstanding parts are made of material having a coefficient of thermal expansion not greater than 10' per C. at l00C.

15. A mount according to claim 10 in combination with a knife holder in the form of a block recessed in its upper face to receive a triangular section knife seated therein with its cutting edge portion extending above said block, said block being provided with second clamp means coupled with one side wall of said block and passing therethrough to said recess to secure said knife against the opposed side wall of said block.

16. A mount according to claim 15 wherein the first mentioned and second clamp means comprise respective bolts, and said knife holder is dimensioned for disposition and securement in said cradle with said bolts substantially axially aligned in said plane. 

1. A microtome knife mount formed with a trough for coolant and provided with a heater, the mount, including trough and heater, being symmetrical about a plane therethrough and adapted to support a knife by way of a connection disposed between said trough and heater and in said plane.
 2. A mount according to claim 1 comprising a base, two mutually spaced upstanding parts extending from one portion of said base to define a cradle with said base portion therebetween as the cradle floor and said upstanding parts as the cradle sides, a cavity formed in the remaining portion of said base to define a trough for liquid coolant, clamp means coupled with one of said upstanding parts to secure a knife in said cradle against the other of said upstanding parts, said base, upstanding parts, trough and clamp means being symmetrical about a common medial plane therethrough.
 3. A mount according to claim 2 wherein said base is of generally slab form having said one upstanding part extending from one end of one major face thereof, said other upstanding part in the form of a wall extending from and across the intermediate region of said one major face, and said cavity formed in the other end of said one major face.
 4. A mount according to claim 2 comprising a thermoelectric transducer housed in said mount, said transducer being symmetrically disposed relative to said plane.
 5. A mount according to claim 2 in combination with a knife holder in the form of a block recessed in its upper face to receive a triangular section knife seated therein with its cutting edge portion extending above said block, said block being provided with second clamp means coupled with one side wall of said block and passing therethrough to said recess to secure said knife against the opposed side wall of said block.
 6. A mount according to claim 5 wherein the first mentioned and second clamp means comprise respective bolts, and said knife holder is dimensioned for disposition and securement in said cradle with said bolts substantially axially aligned in said plane.
 7. A mount according to claim 1 of integral construction.
 8. A mount according to claim 1 made of material having a coefficient of thermal expansion not greater than 10 5 per *C. at -100*C.
 9. A microtome knife assembly comprising: a cutting member, a support member for said cutting member, which support member is formed with a trough for liquid coolant, a heater connected with said support member in spaced disposition from said trough, and connector means securing said cutting member to said support member at a position between said trough and said heater, said support member, trough, heater and connector means being symmetrical about a common plane therethrough.
 10. A microtome knife mount comprising: a base, two mutually spaced upstanding parts extending from one portion of said base to define a cradle with said base portion therebetween as the cradle floor and said upstanding parts as the cradle sides, a cavity formed in the remaining portion of said base to define a trough for liquid coolant, clamp means coupled with one of said upstanding parts to secure a knife in said cradle against the other of said upstanding parts, said base, upstanding parts, trough and clamp means being symmetrical about a common medial plane therethrough.
 11. A mount according to claim 10 wherein said base is of generally slab form having said one upstanding part extending from one end of one major face thereof, said other upstanding part in the form of a wall extending from and across the intermediate region of said one major face, and said cavity formed in the other end of said one major face.
 12. A mount according to claim 10 comprising a thermoelectric transducer housed in said mount, said transducer being symmetrically disposed relative to said plane.
 13. A mount according to claim 10 wherein said base and upstanding parts are of integral construction.
 14. A mount according to claim 13 wherein said base and upstanding parts are made of material having a coefficient of thermal expansion not greater than 10 5 per *C. at -100*C.
 15. A mount according to claim 10 in combination with a knife holder in the form of a block recessed in its upper face to receive a triangular section knife seated therein with its cutting edge portion extending above said block, said block being provided with second clamp means coupled with one side wall of said block and passing therethrough to said recess to secure said knife against the opposed side wall of said block.
 16. A mount according to claim 15 wherein the first mentioned and second clamp means comprise respective bolts, and said knife holder is dimensioned for disposition and securement in said cradle with said bolts substantially axially aligned in said plane. 